Referring to FIG. 1, there is depicted a STOL/VTOL free wing aircraft 10 of the invention disclosed in the aforementioned co-pending application, which comprises a fuselage 12, a tail section 14 and a free wing 16 with a propulsion system including an engine 18 at the forward end of the fuselage for driving a propeller 20. As used in this present specification, a free wing or "freewing" is a wing attached to an aircraft fuselage in a manner such that the wing is freely pivotable about its spanwise axis forward of its aerodynamic center. This arrangement enables the wing to have an angle of attack which is determined solely by aerodynamic forces acting on the wing. Rotation of the wing, without pilot intervention, induced by changes in the direction of relative wind over the wing surfaces, causes the angle of incidence between the wing and the aircraft fuselage to vary so that the wing presents a substantially constant angle of attack to the relative wind which, in horizontal flight, enables the aircraft to be essentially stall free.
The free wing 16 is free to rotate or pivot about its spanwise axis 22 forward of its aerodynamic center. Free wing 16 includes left and right wings 16a and 16b extending from opposite sides of fuselage 12; these wings are coupled together to collectively freely pivot about axis 22. The left and right wings 16a,16b may be adjustable in pitch relative to one another as disclosed in the aforesaid application, the relevant disclosure of which is incorporated by reference herein. Aircraft 10 further includes rudders 24 and elevators 26 in tail section 14 which may be controlled in a conventional manner for yaw and pitch control, respectively. Further, while a single propeller for the propulsion system is illustrated at 20 in FIG. 1, it will be appreciated that other types of propulsion systems may be utilized, such as counter-rotating propellers and multi-engine arrangements attached to the fuselage. As used in this present specification, the term "common propulsion system" means the same propulsion system for supplying the necessary thrust for both horizontal and vertical flight operations and is not necessarily limited to a single thrust producing system, such as a single propeller, but could include multiple thrust producing systems such as a pair of engines driving separate propellers, provided that the multiple thrust producing systems are used for supplying thrust in both vertical and horizontal flight modes.
The operation of the VTOL free wing aircraft 10 is as follows. At launch, the aircraft 10 is mounted in a vertical orientation such as depicted in FIG. 1, on a rail system schematically depicted at 60. Rail system 60 may comprise simply a guide or a track with complementary guide or track following members on the aircraft 10 for guiding the aircraft from vertical movement for a limited initial predetermined distance at lift-off. With the engine started and propeller backwash providing an air flow over the wings 16a,16b, aircraft 10 lifts off of launch rail 60. Catapult assists may be provided. Yaw and pitch controls are maintained by rudder 24 and elevator 26, respectively. Roll control is achieved by differential setting of the pitch of the free wings 16a,16b under pilot or computer control or remote control from a remote controller station (not shown). The air flow over wings 16a,16b provides dynamic forces on the wings to control the roll of the aircraft 10 during launch. The wings 16a,16b at launch are freely rotatable and the dynamic pressure on all control surfaces as a result of backwash from the propulsion system is intended to allow roll, pitch and yaw control over the aircraft 10 during the initial phases of vertical launch.
To transition from vertical to horizontal flight, the pilot, computer or remote controller gives a down elevator signal, causing the fuselage to pitch toward a horizontal orientation. By pitching the fuselage, the thrust vector also inclines from the vertical and thus has a horizontal thrust component. As the fuselage pitches toward the horizontal, the horizontal speed of the aircraft increases, causing the freely rotatable wing 16 to rotate relative to the fuselage in accordance with the relative wind. The effects of the relative wind acting on the freely rotating wing 16a,16b quickly overcome the effects of the airflow over the wings from the propulsion system and, with increasing horizontal speed, the wing develops lift. The aircraft 10 soon transitions into horizontal flight in a free wing flight mode.
Should the aircraft 10 lose power during launch or vertical flight, the aircraft will rapidly and automatically transition into a horizontal flight mode with minimum altitude loss. When power is lost, free wing 16 weathervanes into the new relative wind, which would appear to the wing to be coming vertically upwardly from the ground, and thus obtains a leading edge down orientation while the fuselage will be oriented into the relative wind by the action of the rudder and elevators. Because the free wings use positive pitching moment airfoils, the aircraft will quickly transition itself into stable level flight.
During horizontal flight, pitch, yaw and roll control are provided by the elevators, rudders and differentially pivoted wings 16a and 16b. Ailerons may be provided on wing 16 if desired.
To transition from horizontal to vertical flight, the reverse procedure is employed. That is, an up elevator command is given to rotate the fuselage toward a vertical orientation with its nose pointed upwardly. Horizontal speed is thus decreased and a vertical thrust vector is introduced. Accordingly, the relative wind changes and the free wing and fuselage ultimately both rotate into a vertical orientation. If the aircraft resists slowing and does not reduce its forward or horizontal speed sufficiently, the fuselage, by operation of the elevator, could be rotated past vertical so that the thrust line serves as a thrust reverser, slowing the aircraft past stall. Alternatively, the mechanism of prior co-pending application Ser. No. 07/795,329, filed Nov. 20, 1991, entitled "Lockable Free Wing Aircraft," the disclosure of which is incorporated by reference herein in its entirety, may be utilized. That is, the wing could be locked to the fuselage before rotating the fuselage up. By stalling the aircraft and, hence, achieving a reduction to zero forward horizontal air speed, followed by release to the free wing state upon stalling, the aircraft may be positioned in the vertical orientation. A further alternative to reduce horizontal speed while transitioning from horizontal to vertical flight is to provide wing devices such as spoilers or elevators at the trailing edge of the wing. Still further, a canard could be located in the nose of the fuselage to provide leverage to the fuselage to transition to the vertical. A canard, of course, could be recessed within the nose of the aircraft and displaced outwardly of the aircraft at the time of the transition to leverage the fuselage upwardly. The canard, of course, in any event could be a free wing or fixed. Once vertical or near vertical flight is achieved, the pitch, roll and yaw commands again control the position of the aircraft to a location directly over a net 66. When located over the net, the engine is turned off and the aircraft drops into the net.
Since the tail section is fixed to the fuselage and thereby immovable relative to the longitudinal axis and the thrust axis of the fuselage, relatively sophisticated launch (take-off) and recovery (landing) systems are necessary, such as the launch rail system 60 mentioned above for take-off, and netted recovery systems to land the VTOL aircraft 10 such as depicted in FIG. 6 of the prior application, said drawing figure and related written description being incorporated by reference herein in its entirety. In the alternative, extremely long and complex landing gear extending downwardly below the tail section 14 in the vertical flight mode of FIG. 1 would be necessary for STOL and VTOL operations. This type of landing gear (e.g., a so-called moon rocket landing gear) would be extremely expensive and effective for use only on substantially level terrain.
It is accordingly one object of the present invention to provide a free wing aircraft having vertical and short take-off and landing capabilities (STOL/VTOL) and which does not require external launch and recovery systems.
Another object is to provide a STOL/VTOL free wing aircraft having a thrust line movable between vertical and horizontal orientations without affecting the relative horizontal positioning of at least flight control surfaces located in the tail section to enable use of relatively non-complex and short landing gear.